Appendix X (Examples of Potentially Incompatible Waste)

Reference: 40 CFR, Part 264, July 1, 1991.

Many hazardous wastes, when mixed with other waste or materials, can produce effects that are harmful to human health and the environment, such as: (1) heat or pressure, (2) fire or explosion, (3) violent reaction, (4) toxic dusts, mists, fumes, or gases, or (5) flammable fumes or gases.

Below are examples of potentially incompatible wastes, waste components, and materials, along with the harmful consequences that result from mixing materials in one group with materials in another group. The list is intended as a guide to indicate the need for special precautions when managing these potentially incompatible waste materials or components. This list is not intended to be exhaustive.

The generator must adequately analyze wastes to avoid creating uncontrolled substances or reactions of the type listed below, whether they are listed below or not.

It is possible for potentially incompatible wastes to be mixed in a way that precludes a reaction (e.g., adding acid to water rather than water to acid), or that neutralizes them (e.g., a strong acid mixed with a strong base), or that controls substances produced (e.g., by generating flammable gases in a closed tank equipped so that ignition cannot occur, and burning the gases in an incinerator). When in doubt, contact EHS for clarification.

In the lists below, the mixing of a Group A material with a Group B material may have the consequence as noted.

Group 1-A
Acetylene sludge
Alkaline caustic liquids
Alkaline cleaner
Alkaline corrosive liquids
Alkaline corrosive battery fluid
Caustic wastewater
Lime sludge and other corrosive alkalies
Lime wastewater
Lime and water
Spent caustic

Group 1-B
Acid sludge
Acid and water
Battery acid
Chemical cleaners
Electrolyte, acid
Etching acid liquid or solvent
Pickling liquor and other corrosive acids
Spent acid
Spent mixed acid
Spent sulfuric acid
Potential consequences: Heat generation;
violent reaction.


Group 2-A
Zinc powder
Other reactive metals and metal hydrides


Group 2-B
Any waste in Group 1-A or 1-B
Potential consequences: Fire or explosion;
generation of flammable hydrogen gas.

Group 3-A

Group 3-B
Any concentrated waste in Groups 1-A or 1-B
Metal hydrides
SO2Cl2,, SOCl2, PCl3, CH3 SiCl3
Other water reactive waste
Potential consequences: Fire, explosion, or heat generation; generation of flammable gases


Group 4-A
Halogenated hydrocarbons
Nitrated hydrocarbons
Unsaturated hydrocarbons
Other reactive organic compounds
        and solvents


Group 4-B
Concentrated Group 1-A or 1-B wastes
Group 2-A wastes
Potential consequences: Fire, explosion
or violent reaction


Group 5-A
Spent cyanide and sulfide solutions


Group 5-B
Group 1-B wastes
Potential consequences: Generation of toxic
hydrogen cyanide or hydrogen sulfide gas